The invention relates to a fuel system for an internal combustion engine, a vehicle with a fuel system, a method of controlling a fuel system, a computer program, a computer readable medium and a control unit.
The invention can be applied in heavy-duty vehicles, such as trucks, buses and construction equipment. Although the invention will be described with respect to a truck, the invention is not restricted to this particular vehicle, but may also be used in other vehicles such as cars.
Dual fuel engines are arranged to be provided with two fuels of different types. Such engines may provide flexibility and a reduced environmental impact. Examples are disclosed in EP2143916A1 and US2013087124A1. In a dual fuel engine it is desirable to keep the complexity and the cost of the fuel system as small as possible. WO2013087263A1 discloses a fuel system with a high pressure pump for a liquid fuel and a gaseous fuel. The access of the fuels to the high pressure pump is controlled with a non-return valve and a switching valve. However, the system in WO2013087263A1 introduces a risk of the fuels of different types mixing in an undesired manner before reaching the combustion chambers of the engine, e.g. since the fuels share a single conduit downstream of the high pressure pump.
A way to avoid in a dual fuel engine the risk of fuels of different types mixing is to provide two complete fuel injection systems with respective injectors, common rails and high pressure pumps. However, thereby a complex and expensive solution is provided.
It is desirable to provide a fuel system for a dual fuel engine in which the risk of fuel of separate types mixing is minimized. It is also desirable to provide a fuel system with a minimized fuel mixing risk, which presents a low complexity and therefore a low cost.
According to an aspect of the invention, a fuel system for an internal combustion engine is provided comprising
a first fuel container for a first fuel, a second fuel container for a second fuel, a pump, and a first fuel injector, the fuel system being arranged to provide a communication between the first fuel container and the pump and between the pump and the first fuel injector,
characterized in that the fuel system further comprises a reservoir with a separation device adapted to divide the reservoir into a first volume and a second volume, whereby the separation device may be moved or flexed by a pressure difference in the first and second volumes so as to change the sizes of the first and second volumes,
wherein the fuel system is arranged to provide a communication between the pump and the first volume, and to provide a communication between the second fuel container and the second volume and between the second volume and a second fuel injector.
It is understood that the first the first fuel container is connected to the pump. The first fuel container may be connected to the pump via a first fuel supply conduit. The pump is suitably arranged to pressurize first fuel from the first fuel container. It is also understood that the pump is connected to the first fuel injector. The pump may be connected to the first fuel injector via a first high pressure conduit. The first fuel injector is suitably adapted to inject the first fuel, pressurized by the pump, to be combusted in the engine. It is further understood that the separation device divides the reservoir into the first volume and the second volume. The pump is connected to the first volume, e.g. via one or more conduits and a first valve arrangement as exemplified below. Also, it is understood that the second fuel container is connected to the second volume, e.g. via a second fuel supply conduit as exemplified below. The second volume is connected to the second fuel injector, e.g. via a second high pressure conduit as exemplified below. The second fuel injector is suitably adapted to inject the second fuel from the second fuel container to be combusted in the engine. Where the engine comprises a plurality of cylinders, first and second common rails may be provided to distribute the first and second fuel, respectively, to a plurality of first and second fuel injectors, respectively, as exemplified below.
The pump may be a high pressure fuel pump. The pump may be of any suitable design, e.g. a piston pump or a rotational pump.
It is understood that by the separation device being moved or flexed the first volume may increase in size while the second volume decreases in size, and vice versa. Thus, since the fuel system is arranged to provide a communication between the pump and the first volume, and to provide a communication between the second fuel container and the second volume and between the second volume and a second fuel injector, the first fuel may be pumped to the first volume and used as a working fluid to move or flex the separation device to pressurize and move the second fuel from the second volume to the second fuel injector.
More specifically, a variation of the pressure in the first volume generated by the pump or by a first valve arrangement as exemplified below, provides for a reciprocal movement of the separation device, it turn generating a pumping action of the reservoir to pump the second fuel from the second fuel container to the second fuel injector. Thereby, the fuel system may provide for a single high pressure fuel pump being used for delivering two fuels to the cylinder(s) of the engine. This is advantageous since high pressure fuel pumps are costly. Also, the reservoir provides for separate conduits for the fuels, upstream as well as downstream of the reservoir. Thereby the fuel system may guarantee that the fuels remain un-mixed and delivered separately to respective injectors, e.g. via respective common rails where the engine is provided with more than one cylinder.
In summary, the first fuel provides, in addition to supporting combustion processes in the cylinders, a function of working fluid for pumping of the second fluid by means of the reservoirs. This means that only one high pressure pump needs to be provided for both fuels. This in turn reduced complexity and cost of the fuel system. In addition, by the reservoirs with the separation devices, a separation of the first and second fuels is secured.
In addition, the invention provides the advantage that since the second fuel does not come into contact with the pump, the fuel type choices for the second fuel does not have to be limited to fuels which exhibit favorable properties for such contact. Thus, it is possible for the second fuel to be a fuel with poor lubrication properties and/or an unfavorable viscosity, which are properties that could damage the pump should the pump be in contact with such a fuel, More specifically, since communications are provided between the first fuel container and the pump, between the pump and the first volume, and between the second fuel container and the second volume, the reservoir provides a pumping function for the second fuel under the action of the first fuel as a work fluid. Thereby, the second fuel is pumped by the reservoir without being in contact with the pump.
Preferably, where the pump presents an inlet and an outlet, the communication between the pump and the first fuel injector being provided between the outlet and the first fuel injector, the communication between the pump and the first volume being providable between the outlet and the first volume. The communication between the first fuel container and the pump may be provided between the first fuel container and the inlet, and the communication between the pump and the first volume may also be providable between the inlet and the first volume. Thereby, the pump inlet may be receive first fuel from the first fuel container as well as from the first volume. Also, the pump outlet may be branched towards the first fuel injector as well as towards the first volume. This provides an advantageous manner of implementing the use of the first fuel as a working fluid for pumping the second fuel by means of the reservoir.
Preferably, where the pump presents an inlet and an outlet, a first valve arrangement being arranged to control the communication between the pump and the first volume alternatingly as a communication between the outlet and the first volume and as a communication between the inlet and the first volume. Thereby, the first valve arrangement may provide an effective manner of controlling the pump action of the reservoir. More specifically, by alternating between the communication between the outlet and the first volume whereby the separation device is moved or flexed so as for the first volume to increase in size, and the communication between the inlet end the first volume whereby the separation device is moved or flexed so as for the first volume to decrease in size, the resulting reciprocal size change of the second volume provides effectively provides the pumping action of the second fuel via the second volume.
Suitably, a second valve arrangement is arranged to, when the separation device is moved or flexed so as for the second volume to increase in size, allow the communication between the second fuel container and the second volume and block the communication between the second volume and the second fuel injector. The second valve arrangement is further preferably arranged to, when the separation device is moved or flexed so as for the second volume to decrease in size, block the communication between the second fuel container and the second volume and allow the communication between the second volume and the second fuel injector. Thereby, the reservoir pumping action of the second fuel from the second fuel container to the second injector will be effectively supported.
In some embodiments, the reservoir presents a first portion, in which the first volume is provided, and a second portion, in which the second volume is provided, wherein the first portion presents a first cross-sectional area and the second portion presents a second cross-sectional area which is different from the first cross-sectional area. Thereby, the separation device may comprise a first separation element in the first portion of the reservoir, and a second separation element in the second portion of the reservoir. The first separation element may be separated from the second separation element by a fluid.
It is understood that the first and second cross-sections are perpendicular to direction of movement or flexing of separation device. Such an arrangement with two different cross-sections of the reservoir provides for delivering the first and second fuels at the first and second injectors, respectively, at different pressures. This is beneficial since in many dual fuel combustion applications, the fuels are suitably provided to the engine at different pressures, e.g. due to different performance or compositions of the fuels and different rolls in the combustion process in the engine.
In addition, separating the first and second separation elements by a fluid provides a leakage buffer which will reduce or eliminate the risk of the first and second fuels mixing. It should be noted that the separation elements may be provided in any suitable form, e.g. as pistons or membranes, as exemplified below. It is also conceivable that one of the separation elements in the reservoir is of one type, e.g. a piston, while the other of the separation elements is of another type, e.g. a membrane.
In preferred embodiments, said reservoir, separation device, first volume and second volume are a primary reservoir, a primary separation device, a primary first volume and a primary second volume, respectively, the fuel system also comprising a secondary reservoir with a secondary separation device adapted to divide the secondary reservoir into a secondary first volume and a secondary second volume, whereby the secondary separation device may be moved or flexed by a pressure difference in the secondary first and second volumes so as to change the sizes of the secondary first and second volumes, wherein the fuel system is arranged to provide a communication between the pump and the secondary first volume, and to provide a communication between the second fuel container and the secondary second volume and between the secondary second volume and the second fuel injector.
Thereby, where the pump presents an inlet and an outlet, a first valve arrangement may be arranged to control the communications between the pump and the primary first volume and the pump and the secondary first volume alternatingly as on one hand a communication between the outlet and the primary first volume and a simultaneous communication between the inlet and the secondary first volume, and on the other hand a communication between the inlet and the primary first volume and a simultaneous communication between the outlet and the secondary first volume. Also, a second valve arrangement may be arranged to, when the primary separation device is moved or flexed so as for the primary second volume to decrease in size and the secondary separation device is moved or flexed so as for the secondary second volume to increase in size, block the communication between the second fuel container and the primary second volume, allow the communication between the primary second volume and the second fuel injector, allow the communication between the second fuel container and the secondary second volume, and block the communication between the secondary second volume and the second fuel injector. The second valve arrangement may be arranged to, when the primary separation device is moved or flexed so as for the primary second volume to increase in size and the secondary separation device is moved or flexed so as for the secondary second volume to decrease in size, allow the communication between the second fuel container and the primary second volume, block the communication between the primary second volume and the second fuel injector, block the communication between the second fuel container and the secondary second volume, and allow the communication between the secondary second volume and the second fuel injector.
By such an arrangement of two reservoirs, second fuel may be pumped to the second injector alternatingly from the primary second volume and the secondary second volume. This provides to a steady flow of second fuel to the second injector, with small or moderate changes in the pressure of in the second injector. In other words, a continuous pump activity is provided due to the alternating feeding of the two reservoirs.
Preferably, where the pump presents an inlet and an outlet, the fuel system further comprises a supply valve being arranged to control the communication between the first fuel container and the pump. Where the communication between the pump and the first volume is providable between the inlet and the first volume, and the pump inlet may receive first fuel from the first fuel container as well as from the first volume, the supply valve may be controlled to secure that the supply of first fuel from the first fuel container is the same as the supply of first fuel to the first injector, and that the amount of first fuel provided to the first volume is the same in each cycle of the reservoir.
According to another aspect of the invention, a method of controlling a fuel system for an internal combustion engine is provided comprising
a first fuel container for a first fuel, a second fuel container for a second fuel, a pump presenting an inlet and an outlet, a first fuel injector, a second fuel injector, and a reservoir with a separation device adapted to divide the reservoir into a first volume and a second volume, whereby the separation device may be moved or flexed by a pressure difference in the first and second volumes so as to change the sizes of the first and second volumes,
wherein the fuel system is arranged to provide a communication between the first fuel container and the pump, between the pump and the first fuel injector, between the second fuel container and the second volume and between the second volume and the second fuel injector, the method comprising
controlling a valve arrangement to allow a communication between the outlet and the first volume, and to block a communication between the inlet and the first volume,
receiving a signal indicative of a location or a degree of deflection of the separation device,
in dependence on said received signal switching the valve arrangement to block the communication between the outlet and the first volume, and to allow the communication between the inlet and the first volume.
By switching the valve arrangement in dependence on said received signal indicative of the location or a degree of deflection of the separation device, an effective and secure manner is provided for obtaining alternating valve arrangement states, providing for a reciprocal movement of the separation device, it turn generating a pumping action of the reservoir to pump the second fuel from the second fuel container to the second fuel injector. Thereby, the advantages described above of providing for a single pump being used for delivering two fuels to the engine, and keeping the fuels un-mixed, are obtained.
The signal may be received in any suitable manner. Advantageous embodiments includes receiving the signal from an inductive sensor arranged to detect the location or a degree of deflection of the separation device, or providing the signal as representing the pressure between the second volume and the second injector, or in the second injector, as exemplified below.
Advantageously the method may comprise, determining an amount of first fuel supplied to the first injector, and in dependence on the determined amount of first fuel supplied to the first injector, controlling the communication between the first fuel container and the pump so as for an amount of first fuel supplied from the first fuel container to the pump is the same as the determined amount of first fuel supplied to the first injector. Thereby, the supply valve may secure that the supply of first fuel from the first fuel container is the same as the supply of first fuel to the first injector, and that the amount of first fuel provided to the first volume is the same in each cycle of the reservoir.
For example, the received signal may indicate that the separation device has reached an end of its movement, at which end the first volume is at its maximum size. Thereby, when the valve arrangement is switched to allow the communication between the inlet and the first volume, a supply valve may be controlled to block the communication between the first fuel container and the pump inlet. Before the first volume is at its minimum size, the supply valve may be controlled to open the communication between the first fuel container and the pump inlet. Timing of this opening of the supply valve is thereby based on said determined amount of first fuel supplied to the first injector.
Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims.